LOS ANGELES, California (Reuters) --NASA scientists are excitedly speculating that discoveries made by a Mars rover over the weekend will help them finally unravel whether water played a role in the red planet's geologic history, a science team member said on Monday.

Scientists were poring over data and microscopic images returned to Earth by the rover Opportunity, which spent the weekend examining a multilayered rock nicknamed El Capitan embedded in the side of the small crater where Opportunity landed on January 24.

The rover has yet to climb out of the small crater onto the flat Meridiani Planum to examine a large deposit of what may be water-formed hematite.

The science team planned to command the rover to use a rock scraping tool to clear away dust so that its spectrometers can get clearer readings of El Capitan, which lies in an outcrop of bedrock that scientists believe holds the key to the planet's past.

"There are high expectations that we will understand the extent to which the outcrop has been modified chemically and whether water was involved," said Ray Arvidson, deputy principal investigator.

Arvidson said scientists are working on competing theories about how the fine layers in the meter-high (3-feet-high) outcrop were formed, and hoped to have preliminary findings within days.

"One idea is that it's associated with ash fall or simply windblown material that was compacted," he said. "Or it's associated with [sedimentation in] an old lake or shallow sea. The hope is in the end you have the information to show how they were formed and modified."

Spirited away

On the other side of the planet, Opportunity's twin, Spirit, left the trench it dug and spent days examining, and rolled toward Bonneville Crater, about 100 meters (328 feet) from its landing site in Gusev Crater -- a massive depression the size of the U.S. state of Connecticut.

Preliminary data showed that the soil at the sides and bottom of the trench was "coherent" but scientists were not yet sure what was holding the fine particles together, Arvidson said.

Mission manager Rob Manning said Spirit spent its 49th Martian day, or sol, wrapping up its work in the trench and driving 18.8 meters (62 feet) toward an area nicknamed Middleground, about halfway between Bonneville Crater and the rover's landing point.

The boulder-strewn landscape becomes more treacherous the closer Spirit gets to the crater, which ejected boulders into the surrounding area when a meteor slammed into it eons ago, Manning said.

"We may see craters launched off from well below Gusev crater that may have had some contact with ancient water," Manning said.

Copyright 2004 Reuters. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.